Cycles - transparent background still renders background color through glass?
Under Render>Film you can check 'Transparent' and afterwards 'Transparent Glass'. It may be possible that you are using a blender version, which doesn't have this option. If you aren't bound to any particular version I suggest downloading a Daily Build from https://builder.blender.org/download/

I tried with MixShader (Transparend BSDF and Glass BSDF) and just Glass BDSF, both of them work for me.

The cubes are actually transparent, but it of course then must take some background here in the stackexchange.

Edit, because question was edited:


Enable 'Transparent'
Enable 'Transparent Glass'
Disable 'Transparent'


This way 'Transparent Glass' is enabled without making the background transparent (Imgur has problems with BSE so direct link: https://imgur.com/a/2TSKsfe)